The present invention relates to a molding machine with a stationary platen and a movable platen which combines the functions of mold break and clamp stroke (opening and closing the movable platen) in one unit. The advantages of this system include faster mold break action and reduced overall build length of the clamp assembly.
Injection molding machines are well known which include securing and clamping assemblies, such as for use with the tiebars of both singular and tandem injection molding machines. Thus, the prior art includes many types of tiebar gripping and clamping assemblies for use with injection molding machines. The gripping of the tiebars via these assemblies allows for a high clamping force to be applied to the mold halves during injection molding. For example, typical tie bar gripping and mold clamping mechanisms are shown in the patents to Fukuzawa et al. U.S. Pat. No. 5,135,385; Romi U.S. Pat. No. 5,275,550; Hirata U.S. Pat. No. 5,238,394; and Kushibe et al. U.S. Pat. 4,874,309. In each of these patents a tiebar gripping mechanism and mold clamping unit is disclosed where the tiebar is gripped by clamping devices.
The requirement for forcing open a mold is well known. After filling a closed and clamped injection mold with plastic, the plastic inside the mold is cooled and the cooling of the plastic causes the plastic to shrink to the mold core. Sometimes a considerable force, for example, up to 10% of the mold's required clamping force, is required to break open the mold. This initial motion overcomes the sticking force or stiction that prevents the initial opening of the mold. Once mold break is achieved, or the mold is broken, the mold can easily be opened the remainder of the required stroke obtained. Thus, there is a need for a significant initial mold opening or mold break force and short mold opening movement when opening the mold.
Two platen clamps have typically provided this mold break force with a separate, dedicated cylinder acting directly on the tiebar ends, as shown for example in German Patent 3034024, or by using the mold clamping force in reverse as shown in U.S. Pat. 5,645,875 to Glaesener et al.
Other methods to accomplish this include making the clamp stroke cylinders, usually separate from the clamping cylinders, large enough to provide the required mold break force. However, this requires using a larger diameter cylinder than would be necessary to move the platen which is inconvenient and cumbersome.
Accordingly, it is a principal object of the present invention to provide an improved apparatus and process for clamping a mold.
It is a further object of the present invention to provide an apparatus and process as aforesaid that conveniently and expeditiously applies mold stroke force and mold break force, including fast mold break action and reduced overall build length of the clamp assembly.
Further objects and advantages of the present invention will appear hereinbelow.